Scientists develop technology to recycle used clothing rather than just burning it

When you go running in the woods in your running tights, the spandex is why they fit so comfortably. Elastane is an elastic material that allows the fabric to stretch and conform to your body.

But when spandex fibers are mixed with cotton, wool, nylon or other fibers, as is the case in many garments today, the clothes become almost impossible to recycle. It is extremely difficult to separate the different fibers and therefore clothing materials cannot be recycled.

For this reason, clothing and other textiles are among the materials we are least able to recycle. Only around 6% of clothes thrown away by Danish households are recycled. In comparison, 32% of all plastic packaging is recycled in Denmark.

But that could change, says Assistant Professor Steffan Kvist Kristensen from the Interdisciplinary Center for Nanoscience at Aarhus University. With several colleagues, he is at the origin of a new technology allowing the separation of fibers from mixed fabrics. The work is published in the journal Green chemistry.

“We have developed a method to completely remove spandex from nylon. We’re not there yet with cotton, because some cotton fibers are degraded in the process. But we believe that with some minor adjustments, we “We can solve this problem. this problem,” he says and continues:

“In other words, we can take the fabric apart so we can recycle many more textiles in the future.”

Heat clothes in a large pressure cooker

It is not easy to separate spandex from other fibers once they have been woven together. Clothing is made by wrapping main fibers, such as nylon or cotton, around elastane fibers, which are made of long chains of molecules.

The fibers only break if you break the long chains of molecules, explains Steffan Kvist Kristensen. “The many links in the spandex chain are held together by a small molecule called diamine. By heating the clothes to 225 degrees Celsius and adding a specific alcohol, we found a method to break the bonds in spandex .When this happens, the chains collapse and the materials separate.

“The whole process takes place in what is actually a large pressure cooker that we introduce the textiles into. We then add a little alcohol and a little base and heat it up. Then we let it cook for a little over four hours, and when we open the lid again, the different fibers will have been separated.”

Invented during World War II

When the Japanese attacked Pearl Harbor on December 7, 1941, the United States not only lost several thousand soldiers, hundreds of aircraft, and many of its largest warships. The country also lost access to around 90 percent of the natural rubber on which it was so dependent. Therefore, like the Germans, they began to produce synthetic rubber.

After the war, the production of synthetic rubber led to the discovery of a number of derived synthetic fibers that could be used in textiles. One of these fibers was elastane.

In 1958, chemist Joseph Shivers invented elastane, or Spandex as it is also often called in the United States. Since then, elastane has been increasingly used in our clothes.

The Secret Ingredient Is Drain Cleaner

Since most clothing fibers must be recyclable, using harsh chemicals is not an option for Steffan Kvist Kristensen and his colleagues. Instead, they use alcohol and add a potassium hydroxide base.

“Potassium hydroxide is one of the main ingredients in regular drain cleaners. We found that adding it speeds up the process. It just increases the speed of the chemical reaction,” he says.

He’s not sure why this happens, but it breaks the bonds of the spandex.

“We’re pretty sure that potassium hydroxide increases the reactivity of our alcohol. Either that or the bonds are broken slightly by the potassium hydroxide, so it’s easier for the alcohol to break them completely,” says -he.

I hope the clothing industry adopts technology

So far, Steffan Kvist Kristensen and his colleagues have only experimented with two nylon stockings at a time. The technology is therefore not yet ready to be implemented on an industrial scale. This will require being able to break down much larger quantities of clothing.

“We can only expand things slightly due to the limitations of our equipment, so it’s up to the industry to embrace the technology and seriously develop it,” he says.

However, according to Steffan Kvist Kristensen, Denmark currently does not have the necessary facilities to exploit this technology on a large scale. For that, you will have to look south of the border. “The chemical industry in Denmark is small, but Germany has some of the largest factories in the world. They will most likely be able to use our method to recycle large quantities of fibers from clothing containing elastane.

“If we want to succeed, we need to get the big chemical plants involved. But they need to see a business model in buying recycled materials and using them in the production of new fibers. If not, the technology won’t will never take off.”